The invention relates to a method and apparatus for use in steel reinforced concrete construction. In particular, the invention relates to a clamp for reinforcing a plurality of reinforcing bars assembled into formwork for use in steel reinforced concrete construction.
One of the most prevalent articles used to reinforce concrete structures is a steel reinforcing bar, commonly abbreviated and referred to as xe2x80x9crebar.xe2x80x9d Rebar is useful in constructing a variety of residential and commercial structures to include buildings, foundations for buildings, high-rise hotels, driveways, residential home slabs, dams, parking garages, retaining walls, bridges, and sidewalks. Specifically, rebar is used to reinforce concrete structures exposed to heavy tensile, compressive, and shear stresses. Operators generally require rebar that is ductile and resilient because rebar is generally bent and shaped to conform to a desired structural form. Accordingly, rebar is manufactured by a mill heat treatment process that imparts these desired traits. Further, rebar is routinely galvanized (i.e., coated with rust resistant zinc) prior to incorporation into a structure in order to improve its resistivity to corrosion and to minimize the environmental factors affecting the durability of the rebar (e.g., temperature extremes).
Conventional rebar is milled into cylindrical rods optionally including a number of longitudinal ribs and crescent shaped ribs forming a helical pattern (i.e., threaded or spiral pattern) extending the length of the bar and transverse to the longitudinal ribs. The longitudinal ribs and crescent shaped ribs are generally of uniform height. The transverse ribs are also inclined at a desired angle relative to the longitudinal axis of the rebar. The helical ribs formed on the exterior of rebar are capable of engaging a variety of devices used to secure or strengthen the structure (e.g., correspondingly threaded nut or flexible tie wire). In addition, characteristic markings consisting of small longitudinal or inclined ribs spaced at varying intervals along the rebar are used to enable construction workers to identify particular workpieces assembled from rebar.
The type of reinforcing technique used in concrete construction depends upon the forces to which the structure will be exposed. For example, reinforcing steel mesh is often suitable for low stress applications such as a small retaining wall along an embankment. Further, the flexibility of the steel mesh allows operators to incorporate the mesh into a shaped structure in a relatively easy fashion. In other words, reinforcing steel mesh is easily cut and shaped to conform to a structure. In contrast, structures exposed to high tensile and compressive forces require a set of rigid forms or pieces (e.g., rebar) of sufficient strength to reinforce concrete forms such as walls or floors. As is known to those familiar with reinforced concrete construction, the set of forms used in constructing concrete reinforced structures is known as formwork. The formwork resembles a grid-like pattern forming the shell (or superstructure) of a building constructed of steel reinforced concrete. Rebar formwork is generally visible during the construction of high-rise buildings. The limited amount of square footage in heavily populated cities demands that engineers construct highrise office buildings and multi-level parking decks of rebar formwork. The incorporation of rebar into these structures occurs at nearly every stage of construction.
For example, large high-rise buildings require solid foundational supports formed of piers (i.e., vertical support structure). The piers are formed by drilling circular shafts into the ground, constructing a circular cage of rebar by entwining rods of rebar in a spiral fashion around vertically extending rods of rebar, positioning the circular cage of rebar in the drilled shafts, and then filling the shafts with wet concrete. The concrete eventually sets and engineers are then able to proceed with construction by incorporating rebar formwork in the structure in an upward direction. Examples of rebar cages used in drilled shafts include drilled piers, caissons, cast-in-drilled-hole piling, and cast-in-place piles.
As described previously, rebar formwork is also used in the construction of vertical walls and foundation slabs. A conventional method for incorporating rebar formwork into concrete construction to form a vertical structure (e.g., wall) includes securing one end of a set of parallel, vertically extending reinforcing bars to the foundation of a structure and thereafter securing a set of parallel, horizontally extending reinforcing bars perpendicular to the vertically extending reinforcing bars. The resulting lattice arrangement (i.e., the formwork) is subsequently encased by a forming system that includes steel rails, cross members, and steel or wood panels, such as the forming systems sold under the trademark STEEL-PLY(copyright) and VERSIFORM(copyright). Thereafter, concrete is poured into the encasement and around the formwork. Once the concrete sets, the components of the forming system (i.e., rails and panels) are removed, thus revealing a steel reinforced concrete vertical wall. The process of encasing formwork and pouring concrete continues in an upward fashion until a desired height is reached.
Similarly, formwork can be assembled on a flat surface adjacent the construction site and then lifted to a desired section of the building under construction. This method includes arranging a series of parallel reinforcing bars on the ground near the construction site and then overlaying another series of parallel reinforcing bars on top of and perpendicular to the previously arranged reinforcing bars. Intersections formed by the intersecting portions of overlapping reinforcing bar are then tied together by strapping material or wire. Typically, those assembling the formwork out of rebar must determine the length of reinforcing bar required for the specific job (e.g., retaining wall or building siding), cut the pieces of rebar into the required lengths, and then bind the individual pieces of rebar into a desired arrangement. The formwork is then lifted by a crane or other conventional lifting means to a desired height (e.g., to an upper-level of a multi-level building). Unfortunately, the lifting of the formwork places stress upon the intersections of the reinforcing bar. Thus, many construction workers opt to weld a number of the intersections of reinforcing bar in order to ensure that the formwork assembly retains its arrangement during lifting. The welding step, in particular, is time consuming and requires a trained welder. Further, the welding process results in overall downtime during the construction process.
Upon reaching the desired height, the formwork is lashed or tied to the building""s superstructure and the formwork is encased by steel rails, cross-members, and panels of the above-referenced forming system. Concrete is then poured into the encasement form and around the rebar formwork, resulting in a steel reinforced concrete vertical wall once the concrete sets and the encasement form is removed.
Rebar may also be used to construct a concrete foundation or sidewalk in a similar manner by arranging a series of parallel reinforcing bars on the foundation of the slab or sidewalk to be constructed and then overlaying another series of reinforcing bars on top of and perpendicular to the previously arranged reinforcing bars. Thereafter, the rebar is tied together at their intersections and concrete is poured onto the rebar formwork. This method is used to form, for example, the foundation of a single story structure as well as an intermediate foundation of a multi-story building that serves as both the floor and roof of adjoining levels.
Advantageously, rebar can be recycled by stripping the surrounding concrete from the outer surface of the rebar. Thereafter, the rebar can be remilled and then incorporated into a different structure.
Nevertheless, the conventional methods described above fail to provide sufficient support to the rebar formwork when the formwork is lifted or transported from the assembly site to the construction site. In particular, the conventional method of lifting the assembled formwork secured by wire pieces directs an inordinate amount of stress to the wire bound intersections of reinforcing bar. In other words, the stress placed on the piece of rebar that is connected to the crane is directed to the wires binding the adjacent intersections. The wires tend to snap under the concentrated stress in a cascading fashion along the length of the formwork. Accordingly, the falling pieces of rebar destroy the structural integrity of the formwork. Further, individual pieces of rebar or sections of bound rebar falling from the raised formwork may damage the superstructure and cause bodily harm to any construction workers who may be in the path of the falling debris. Further, the remaining rebar is often bent beyond repair and has to be discarded.
Therefore, there is a need for a means for stabilizing the reinforcing bars assembled into formwork for use in steel reinforced concrete construction.
Therefore, there is also a need for a means for reinforcing formwork for use in steel reinforced concrete construction so that the formwork retains its structural integrity during transportation.
Further still, there is a need for a method for constructing formwork for use in steel reinforced concrete construction whereby the formwork maintains its structural integrity when the formwork is transported from an assembly site to a construction site.
The invention meets these objectives with a device for fixing reinforcing bar formwork in a desired configuration such that the configured formwork maintains its structural integrity when the formwork is lifted. In particular, the device is a clamp that secures two overlying reinforcing bars at an angle to one another at the intersection of the two bars. The clamp includes a plate with at least two gripping positions on opposite sides of the intersection of the reinforcing bars that grips one reinforcing bar between another reinforcing bar and the plate. A recessed channel on one face of the plate cradles the reinforcing bar sandwiched between the plate and the other reinforcing bar. The gripping positions on opposite sides of the intersection of the reinforcing bar distribute the majority of the weight of the formwork from the intersection to the plate, thus reducing the load bearing forces acting on the intersection of the reinforcing bar when the formwork is lifted. Advantageously, the reduction of force acting on the intersection reduces the likelihood that the formwork will bend or break.
Another goal of the present invention is to develop a method of constructing formwork for used in concrete construction wherein reinforcing bar is arranged in a desired assembly and reinforced by clamping the bars together with the present invention at selected intersections and then lifting the reinforced formwork to a desired location.
In sum, the advantages of the present invention mentioned above eliminate the multiple steps discussed in the conventional methods (i.e., cutting and welding of rebar) and therefore increase efficiency of the entire process.